AR15 build questions (upper)

Did you use an action block. https://www.youtube.com/watch?v=5KyOeY_tAng

If things bound up as tight as you say, it should have been obvious what parts were not aligned. Even if the gas tube doesn't line up perfectly with the key, it won't jam solid like that. You may have inserted the bolt without the firing pin in place. That will lock it up. Barrel nut is not critical as long as the gas tube can be straight.

Did accidentally over tightening the barrel nut but about 1/4 turn do any damage?

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I do not know how you can overtighten the barrel nut by a quarter of a turn and not have completely stripped the threads off the receiver. I suspect you meant to say something other than that what you wrote.

Having said that, it is unlikely that over tightening the barrel nut will cause the barrel extension and the bolt to misalign. It is entirely possible that the receiver may not be perfectly true, and that the bolt face may not be entirely true, and the combination of tolerance stacking caused the bolt to stick in the extension. I have had a few builds where the bolt was difficult to manually retract until everything had the opportunity to burnish in a bit.

my guess is that you did not center the barrel nut, and the gas tube is off to one side, that is very common. it makes the snorkel in the carrier bind in the gas tube. You just look into the reciever with the bolt out, and make sure the gas tube is more or less centered. It doenent have to be perfect, but its not too hard to get it perfect.

As stated above, a slightly misaligned gas tube will not lock up the action and require the removal of the barrel to correct. An AR upper will cycle fine without any lube and a dry upper will not jam up the action tight like that.

Too bad there aren't photos. Assuming parts were installed correctly.... Again, if you toss the BCG in without the firing pin, the bolt lugs can lock and have no reason to unlock. The reason for this is that the cam pin can rotate into a position that prevents the bolt from unlocking. Then, you have an ugly problem on your hands. But, I've never had to remove the barrel to correct that mistake.

As stated above you can't over tighten the barrel nut by a quarter turn. If the gas tube won't line up after 35lbs torque you need to back it off and try again. Make sure the threads are lubricated with grease or thread compound.
The bolt carrier should push into the forward position with light thumb pressure. Anything more than that is too much pressure.

At this point I am curious to know the manufacturer of these parts. Since there are so many parts makers all over the world, there are also lots of parts combinations that won't work. A good rule of thumb is to get all the parts from a single reputable source.

WM

Glad to hear you figured it out. Sounds like you are ready to enjoy your build.



Yeah, I also did a double take when you said you accidently turned the barrel nut a quarter turn too far..........were you using a torque wrench when you installed the barrel nut ? Typically, once you get the barrel nut fairly tight and you are getting it aligned; with the proper amount of torque, you MIGHT be able to move it 1/16" or something like that. No way a quarter turn or anything even in that league.

When I build uppers, I have a gas tube thing........a fitting device.........a solid cylinder of aluminum the same size as a gas tube but only something like 4"-5" long, that you use to insert through the barrel nut and into the receiver. Obviously you see if it passes through the hole OK. Then you can eye ball it in the receiver and see if it seems to be centered and parallel to the inside of the receiver (not canted).

After I get the whole thing together, I push the stripped bolt carrier in and out to make sure it doesn't bind and slides back and forth easily. I never lubricated the bolt carrier during this process. The only thing I lubricate is the barrel nut. The bolt carrier should slide in and out with very light finger pressure.